The association of energy and/or protein intake in relation to z-scores

To be able to investigate the association of energy and/or protein intake in relation to the z-scores, there was adjusted for factors influencing the nutritional status, namely fat malabsorption expressed as coefficient of fat absorption and pulmonary function starting out at 6 years old expressed as forced expiratory volume (FEV1) in % predicted by spirometry (FEV1%)4, as possible confounders. In addition, the factors influencing the nutritional status, namely cystic fibrosis transmembrane conductance regular (CFRT gene) mutation , age at diagnosis , , and history of meconium ileus (MI) were checked as possible modifiers .
Statistics
Data was analysed by using SPSS Statistics 22 (SPSS Inc., Chicago, IL) and the significance was described as p-value <0.05. Due to repeated measurements of individual patients at different years of age, the children were stratified according to years of age (0 year = birth < 1 year, 1 year = 1 year-< 2years etc.). All variables were normally distributed.
To find out if there was an association between energy intake and the continue variables of z-scores for weight-for-age, height-for-age, height-adjusted-for-target-height or weight-for-height, the univariate regression analyses was used. The energy intake was expressed as absolute total intake and as kcal/kg/bodyweight. The same analyses were done for the association between protein intake expressed as total intake and % of total energy intake and the z-scores for the nutritional status. In addition a stepwise multiple regression analysis (association model) was performed to correct the association described as above for the confounders and effect modifiers.
To be able to investigate if there were differences in intake of energy and/or protein among patients grouped into categories, the MANOVA and one-way ANOVA and the post-hoc-procedure of Bonferroni were used. For this purpose, the children were categorised on the basis of their nutritional status and the z-scores were divided into five categories: those with a z-score below -2, between -2 and -1, between -1 and 0, between 0 and +1 and those with a z-score above 1. Subsequently the patients were categorized based on the z-scores into those with a z-score above 0 and those with a z-score < 0.

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